A flexible packaging laminated material is used over many years for liquid food packaging. The packaging container for milk, juice, Japanese sake, white distilled liquor, mineral water, and other drinks is manufactured according to the following steps to the container of the final shape: The step of forming the web shape packaging material which has crease lines in fibrous substrates (for example, paper etc.)/ plastic laminate by the longitudinal seal in the long direction at the tube shape, the step of being filled with liquid food in the packaging material formed to the tube shape, the step of traversal sealing in the transversal direction of tube shape packaging material, the step of forming in first shape like a cushion or a pillow, the step of cutting separately at fixed spacing when packaging material is a web shape, the step of folding along with a crease line. The final shape includes a brick shape (parallelepipedic shape), a hexagon column, an octagon column, a decagon column, tetrahedron shape, etc. The material of a fibrous substrate is a paper board in many cases.
The paper packaging container of a gable top shape is obtained according to steps in which paper packaging material is cut in predetermined shape, the blanks which sealed to container lengthwise is obtained, after sealing the bottom of the blanks in a filling machine, the container is filled with the drink of cow's milk and juice from up opening, and the upper part is sealed. The appearance design of a packaging product is printed on the front face of the packaging material.
As for the conventional laminated packaging material used for the paper packaging product, low density polyethylene (LDPE)/printing ink layer/paper core layer (fibrous carrier layer)/LDPE/aluminum foil (gas barrier layer)/LDPE/LDPE, LDPE/printing ink layer/paper core layer/LDPE/LDPE, printing ink layer/LDPE/paper core layer/ LDPE/LDPE, LDPE/printing ink layer/paper core layer/LDPE/aluminum foil/ polyester (PET), etc. are known. They are actually used widely now.
Generally the above-mentioned laminate for packaging is manufactured according to the steps in which the raw-paper roll of a paper core layer is carried in to a printing machine, the raw-paper side is printed, the printed paper is again wound around a roll shape, the paper is sent to an extrusion laminator from the roll, and fused polyolefin (for example, LDPE etc.) are extruded from an extruder to the raw-paper side, when gas barrier layers (aluminum foil etc.) are included, the fused polyolefin is extruded with lamination coating also between the gas barrier layer. When laminating the above gas barrier layers or adding the functional layer of further others, no layers are laminated at once, but separately, partial laminates are prepared, respectively, and are temporarily made into a roll shape, subsequently the partial laminate is laminated, and the final laminate has been obtained.
As for each layer of the above-mentioned laminate for packaging, each has each function and feature. Plastic coating for liquid tight is formed in the both-sides of the fibrous core layer of paper or paper board formed to a packaging container. The plastic coating protects a liquid absorption fibrous core layer from the osmosis by the moisture effectively. The laminated outside layer usually gives the outstanding heat sealability to the packaging material, and consists of thermoplastic matter, such as a low-density polyethylene, as mentioned above.
However, the laminated packaging material which consists only of paper or the paper board, and the above-mentioned thermoplastic outside layer is lacked in a mechanical strength, and is inferior to the barrier against the gas (especially oxygen gas) from the outside of a container. When liquid food is fruit juice of citrus fruits etc. and is preserved in ordinary temperature at a long period of time, the non-scalping and oxygen barrier for the perfume and flavor are needed in packaging. Since oxygen penetrates through the wall of the carton, the liquid food loses the above-mentioned nutritional value. Usually a gas barrier layer is added to a laminate for reduction of permeation of the oxygen to carton, and minimization of degradation of a nutrient like vitamin C.
As mentioned above, in order to maintain the quality of a contents product, a function of preventing that the aroma flavor of a contents product etc. penetrates packaging material, and leaks outside, and a function of preventing that the packaging material in contact with a contents product absorbs the aroma, flavor, etc. or, the non-scalping of preventing a foreign matter etc. oozing out for a contents product from packaging material, and injuring the aroma, flavor, etc., the gas barrier which protects the contents product from the gas (oxygen gas etc.) which injures the quality of contents product in the laminated material wall of a packaging container is needed for packaging material. The packaging material, which fully has the function, a non-scalping, and a gas barrier, is desirable.
The material with the excellent oxygen gas barriers, such as aluminum, foil, EVOH (polyethylene vinyl alcohol) and PVOH (poly vinyl alcohol), and vapor deposited layer of inorganic oxide, is known as gas barrier material which gives the gas barrier to packaging material.
Furthermore, in about 10-4 degree C. refrigeration conditions, it is preferable that a quality storage term (shelf life) is extensible, in recent years. It is desirable to maintain the nutrition and quality of content products, such as vitamin C, after the storage for about 6-8 weeks in 7-4 degrees C., or at about 10-12 weeks or more in about 8 degrees C.
However, as for the conventional gas barrier material, the content of the product in a packaging container suffers damage from the some defects. Moreover, it is timely to substitute other gas barrier material for aluminum foil from a viewpoint of the environment and the recycling.
The aluminium foil is effective as a barrier material. Since use of an aluminium foil will seemingly bring the concern on the environment, the various attempts in which the practical alternative to an aluminium foil is developed have been made. The alternative has the barrier which was excellent in oxygen gas and aroma, and is easily scrapped after use.
Using the vapor deposited layer of an inorganic oxide for the packaging material for paper containers as an alternative of an aluminium foil was proposed (JP Y 05-28190, JP T 08-500068, and JP A 06-93120). By such packaging material, the paper container which has a gas (oxygen) barrier can be provided. However, they are not enough for the above-mentioned non-scalping or quality preservability. Since the vapor deposited layer of an inorganic oxide does not have mechanical strength but a vapor deposited substrate layer retains mechanical strength, unless the vapor deposited substrate layer is multi-functional material, it is necessary to make packaging material into an excessive layer structure. In the meaning, the amount of material of packaging material, the environmental load, and the manufacturing cost increase.
The barrier polymers, such as EVOH, PVOH, etc. as a gas barrier material of the package for food, are very sensitive to the moisture, and the barrier to oxygen gas is quickly lost in the damp atmospheres. Therefore, by another polymer, for example, the polyethylene layer having the water-impermeability, it is necessary to laminate the barrier layer so that gas barrier layers, such as EVOH and PVOH, may be surrounded. In manufacture of the packaging material which contains EVOH, PVOH, etc. as a gas barrier layer, it is necessary to constitute packaging material as a multilayer laminate which has two indispensable protection outer layers which enclose the gas barrier layer. The manufacturing cost is raised by the manufacture.
In order to give the barrier including non-scalping to packaging material or a film, many techniques of laminating polyamide (e.g. nylon) on packaging material or a film are proposed conventionally. (JP A 51-41078, JP A 58-160244, JP A 03-49953, JP A 04-179543, JP A 05-50562, JP A 05-261874, JP A 06-80873, JP A 06-305086, etc.)
JP A 51-41078 (Applicant: International Paper) indicates the laminate for paper containers which has the laminated structure of the polyethylene thermoplastic outermost layer/paper substrate layer/nylon-film layer/polyethylene thermoplastic innermost layer.
JP A 58-160244 (Applicant: Asahi Chemical Industry) discloses the barrier paper container of which laminating structures are the barrier outside film containing nylon/paper/barrier inner film containing nylon.
JP A 03-49953 (Applicant: Solvey) discloses the gas barrier laminating complex for containers which is laminated by the film (the condensation polymer of meta-xylene diamine and abipic acid (aliphatic alpha, omega-dicarboxylic acid), so-called nylon-MXD6) and the paper substrate. The condensation polyamide polymer of meta-xylene diamine and abipic acid is called “nylon-MXD6”. The polymer is semi-crystalline polyamide. Compared with the conventional polyamide, the polymer has specially the excellent gas barrier to oxygen gas, high elongation, good bending strength, high tensile stress, high glass transition temperature, low coefficient of water absorption, etc.
JP A 04-179543 (Applicant: Dai Nippon Printing) proposes the barrier compound paper container of which the laminated structures are paper substrate layer// the above-mentioned nylon-MXD6 layer//adhesiveness polyolefine innermost layer, at least.
JP A 05-229070 (Applicant: Westvaco) discloses the packaging laminate of a paper-board supporting layer, and amorphous polyamide and heat sealable polyolefine innermost layer. The main faults of the packaging laminate are not having a good gas barrier by economical polymer layer thickness, when extending the shelf life. That is, a layer thickness is thick.
JP A 05-50562 (Applicant: Dai Nippon Printing) proposes the barrier compound paper container of which the laminated structure is the paper substrate layer// semi-aromatic polyamide which comprises of copolymer of aliphatic polyamide component and aromatic-polyamide component.
JP A 05-261874 (Applicant: Okura Industrial) proposes the coextrusion multilayer packaging file which comprises the blend-polyamide-resin layer of xylene-diamine polyamide, such as nylon-MXD6, and other polyamide, such as nylon 6, modified polyolefine adhesive layer, and polyolefine layer.
JP A 06-80873 (Applicant: Ube Industries) proposes the resin composition for oxygen barrier packaging films which the stratified silicate (so-called nano clay) distributed uniformly to aliphatic polyamide resin and aromatic polyamide resin. The result of obtaining the resin composite (packaging container) having the toughness of aliphatic polyamide and the tensile properties, and the oxygen gas barrier of an aromatic polyamide and the nano clay is shown.
JP A 06-305086 (Applicant: Mitsubishi Chemical) indicates the paper container which comprises of biaxis-stretch film including the layer which comprises of a blend of aromatic polyamides, such as nylon-MXD6, and two aliphatic polyamide layers, and a paper layer.
JP A 06-305086 describes the laminate from the biaxis-stretch polyamide film and the paper layer, and the polyamide film consists of at least two polyamide layers and at least one layer including nylon-MXD6. By the dry lamination method or extruding lamination using an adhesive, the biaxisly-stretched film is laminated on a paper layer. The biaxis film is beforehand manufactured according to for example, the step of carrying out the blow film moulding, and then the step of laminating in other layers.
In the laminates obtained according to the steps, a urethane adhesive or an acrylic adhesive, polyester adhesive between the paper layer and the polyamide layer must be used. For producing the laminate, the steps need more and/or various materials, therefore result in a high production cost and heavy environmental load. Furthermore, probably the adhesion between the paper layer and the polyamide layer is not good in the laminate. The reason is that the surface of pre-manufactured film is hardened by oxidization and is not easily attached to the joint layer by extrusion. Since the pre-manufactured steps of the biaxial-stretched film are needed especially, in manufacture of the laminate, the method of manufacturing becomes more complicated and has a low cost performance.
Usually, the polyethylene of laminated material used in a liquid food paper packaging container is low density polyethylene (LDPE), and is the high-pressure-process low density polyethylene especially. The low-molecular-weight component contained in the high-pressure-process low density polyethylene of an innermost layer bleeds to the content in a paper packaging container, and when preserving at a long period of time, the taste of the content may change. In the ethylene alpha olefine copolymer obtained using a Ziegler catalyst, if lubricant is added in order to improve high seal temperature and inferior workability, the lubricant will bleed to a content product and will reduce the taste.
The paper-packaging container which uses the linear low density polyethylene (LLDPE) for an innermost layer is proposed (JP A 62-78059, JP A 60-99647, etc.). The linear low density polyethylene is very excellent in impact strength, tear strength, cold brittleness, heat-sealing reinforcement, hot tag nature, etc. However, since heat-sealing start temperature is somewhat high as compared with LDPE, EVA, or an ionomer, the linear low density polyethylene is inferior to converting properties.
On the other hand, the paper packaging container which uses the ethylene alpha olefine copolymer (so-called metallocene PE or mLLDPE) which polymerized with the metallocene catalyst for an innermost layer is proposed. (JP A 07-148895, JP A 08-337237, JP A 09-29868, JP A 09-52299, JP A 09-76435, JP A 09-142455, JP A 09-86537, JP A9-76375, etc.). The metallocene PE being applied to a container according to the low-temperature sealability, the film workability, and a narrow molecular weight distribution, is known (WO 93/08221, Reference “Plastic” vol. 44 No. 1, P60, Reference “Chemistry economy” vol. 39 No. 9, P48, Reference “Plastic” vol. 44 No. 10, P83). However, even though the metallocene PE has the low-temperature sealability and the low concentration of the low-molecular-weight component, an extrusion coating properties of all the metallocene PE in the case of packaging material manufacture is not necessarily shown, therefore the good performance is not shown in the converting properties. That is, practical extrusion coating cannot be obtained by use of the normal metallocene PE.